Project Summary ! Antibiotics that inhibit cell wall synthesis serve as an important strategy to control bacterial pathogens. These molecules prevent expansion of the peptidoglycan sacculus, resulting in the accumulation of cellular contents without associated growth, ultimately leading to cellular lysis. Recently it has been reported that some Gram- positive bacteria respond to cell wall-active antibiotics by stimulating the production of the nucleotide second messenger (p)ppGpp. Since this molecule can inhibit many cellular processes, (p)ppGpp synthesis in antibiotic treated cells reduces overall biosynthesis and thereby potentially lessen the potentially lethal incompatibility of continued accumulation of cellular content and inhibited cell growth. This proposal is aimed at understanding several aspects of this mechanism. First, how does (p)ppGpp specifically act to inhibit cytoplasmic biosynthesis in response to cell wall active antibiotics? And second, how are cell-wall active antibiotics detected ? what is the signal transduction cascade leading to the activation of (p)ppGpp synthesis? Finally, if this homeostatic mechanism facilitates survival in the presence of cell wall-active antibiotics, interference with this mechanism should make the bacteria more sensitive to these compounds. We will therefore use insights gained in investigating these questions to identify molecules that interfere with this mechanism and determine if they alter the sensitivity of the bacteria to cell wall-active antibiotics. !